Ballistic resistant body armor article

ABSTRACT

Disclosed herein are ballistic resistant articles comprising one or more woven fabric layers woven from yarns having a tenacity of at least 7.3 grams per dtex and a modulus of at least 100 grams per dtex and one or more sheet layers comprising a carbon nanotube-polymer composite, the composite comprising randomly oriented carbon nanotubes embedded in a condensation polymer.

FIELD OF DISCLOSURE

Provided are ballistic resistant articles comprising one or more woven fabric layers and one or more sheet layers comprising a carbon nanotube-polymer composite.

BACKGROUND

Many designs for body armor for resisting ballistic threats have been proposed, and many commercialized. Designs are often intended to increase the comfort of the wearer, thereby increasing use of the body armor. Comfort is generally increased by making the body armor lighter and more flexible to allow greater freedom of motion by the wearer. However, apparel weight needs to be increased to provide protection against projectiles having greater velocities and mass.

Standards have been proposed and adopted throughout the world to ensure minimum capabilities of body armor for resisting ballistic objects. See NIJ Standard—0101.06 “Ballistic Resistance of Personal Body Armor”, issued in July 2008, which defines capabilities for body armor for level IIA, II, IIIA, and III protection. To achieve level II protection, the armor must have no penetration and no more than a backface deformation of 44 mm by a projectile such as a 0.357 magnum projectile at a velocity (V_(o)) defined as 1430 ft/sec plus or minus (+/−) 30 feet per sec (436 m/sec+/−9 m/sec). To achieve level IIIA protection, the armor must have no penetration and no more than a backface deformation of 44 mm by a 0.44 magnum or similar projectile at a velocity (V_(o)) defined as 1430 ft/sec plus or minus (+/−) 30 feet per sec (436 m/sec+/−9 m/sec). Body armor is frequently designed with a margin of safety surpassing the requirements of the NIJ Standard. However, increasing the margin of safety typically increases the cost and weight and decreases the flexibility of the body armor. As a result, body armor is typically made to meet published standards with a small margin of safety.

There are also many designs for body armor for resisting spike (e.g., ice pick-like) or knife stabbing or slashing threats. However, such designs typically are not optimum or even necessarily able to protect against ballistic threats. Separate standards have been published providing different tests and requirements for such spike or knife resistant body armor compared to standards for ballistic resistant body armor. Thus, those skilled in the art do not assume teachings on making or optimizing spike or knife resistant body armor are useful in designing ballistic resistant body armor.

Body armor meeting the NIJ ballistic standard level II or IIIA protection can be made solely of woven fabric layers made from high tenacity multifilament yarns, such as made from para-aramid. Such woven fabric layers provide very good penetration resistance against bullets and fragments. However, woven fabric layers alone provide less protection against backface deformation requiring more layers and increased weight to meet the margin of safety or even the standard. Hybrid body armor meeting the level II or IIIA protection can be made using a plurality of such woven fabric layers stacked in combination with a plurality of unidirectional assemblies comprising a unidirectional tape made of an array of parallel high tenacity multifilament yarns in a matrix resin stacked with adjacent tapes with their yarns at angles inclined with respect to adjacent tapes. Typically the yarns in the tapes are at right angles with respect to yarns in adjacent tapes. These hybrid body armors provide good penetration resistance against bullets and greater protection against backface deformation, but replacing woven fabric layers with unidirectional assemblies reduces protection against fragments while increasing rigidity and cost. Body armor meeting the level II or IIIA protection can be made solely using a plurality of the unidirectional assemblies. They provide good penetration resistance against bullets, very good protection against backface deformation, but they typically provide the least protection against fragments, are more rigid than the other options, and are the most expensive.

Various body armor designs are known. For example, U.S. Pat. No. 7,665,149 discloses a body armor article for resisting ballistic objects, comprising: a plurality of woven fabric layers woven from yarns having a tenacity of at least 7.3 grams per dtex and a modulus of at least 100 grams per dtex; a plurality of sheet layers comprising nonwoven random oriented fibrous sheets, each of the sheet layers comprising a uniform mixture of 3 to 60 weight percent polymeric binder and 40 to 97 weight percent non-fibrillated fibers, the non-fibrillated fibers having a yarn tenacity of at least 1.8 grams per dtex and a modulus of at least 75 grams per dtex, and wherein each of the sheet layers has a thickness of at least 0.013 mm; the woven fabric layers and the sheet layers stacked together comprising a first core section which includes at least two repeating units of, in order, at least one of the woven fabric layers then at least one of the sheet layers; and the sheet layers comprising 0.5 to 30 wt % of the total weight of the article.

There is an existing need for improved lightweight body armor designs that provide protection against ballistic threats without increasing the weight (e.g. areal density) of the body armor.

SUMMARY

Provided herein are ballistic resistant articles comprising one or more woven fabric layers and one or more sheet layers comprising a carbon nanotube-polymer composite, the woven fabric layers and the sheet layers stacked together to form a core section comprising one or more of the woven fabric layers and one or more of the sheet layers. The woven fabric layers are woven from yarns having a tenacity of at least 7.3 grams per dtex and a modulus of at least 100 grams per dtex. The carbon nanotube-polymer composite comprises randomly oriented carbon nanotubes entangled to form a planar structure and embedded in a condensation polymer, the composite containing from about 15 weight percent to about 80 weight percent carbon nanotubes based on the weight of the carbon nanotubes and the condensation polymer. In one embodiment, the condensation polymer comprises polyester, polyamide, polyaramid, or polyacetal. In one embodiment, the sheet layers comprise 0.25 weight percent to 15 weight percent of the total weight of the ballistic resistant article.

In one embodiment, the core section has (i) a surface that, in the assembled armor, is oriented towards the first-strike section and is hereinafter referred to as the “core first strike surface”, and (ii) a surface that, in the assembled armor, is oriented towards the body-facing section, and is hereinafter referred to as the “core body-facing surface”, wherein the article further comprises a first strike section and a body-facing section, the first strike section comprising a plurality of the woven fabric layers stacked together and in contact with the core first strike surface, and the body-facing section comprising a plurality of the woven fabric layers stacked together and in contact with the core body-facing surface.

BRIEF DESCRIPTION OF THE FIGURES

The ballistic articles disclosed herein are described with reference to the following figures.

FIG. 1 is an exploded perspective view of one embodiment of a ballistic resistant article comprising, in order, a first strike section, a core section comprising four repeat units wherein each repeat unit comprises one or more woven fabric layers and one or more sheet layers, and a body-facing section.

FIG. 2 shows a first manner for attaching layers together.

FIG. 3 shows a second manner for attaching layers together.

FIG. 4 shows a third manner for attaching layers together.

FIG. 5 shows the stitching pattern for attaching layers together used in Examples 10, 11, and 12.

FIG. 6 provides a diagram of the pressing package used to generate the carbon nanotube-polymer composites of Examples 1 through 9.

FIG. 7 shows a cross section of the ballistic resistant article of Example 10.

FIG. 8 shows a cross section of the ballistic resistant article of Example 11.

FIG. 9 shows a cross section of the ballistic resistant article of Example 12.

DETAILED DESCRIPTION

As used herein, where the indefinite article “a” or “an” is used with respect to a statement or description of the presence of a step in a process of this invention, it is to be understood, unless the statement or description explicitly provides to the contrary, that the use of such indefinite article does not limit the presence of the step in the process to one in number.

As used herein, when an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.

As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains” or “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

As used herein, the term “about” modifying the quantity of an ingredient or reactant employed refers to variation in the numerical quantity that can occur, for example, through typical measuring and liquid handling procedures used for making concentrates or use solutions in the real world; through inadvertent error in these procedures; through differences in the manufacture, source, or purity of the ingredients employed to make the compositions or carry out the methods; and the like. The term “about” also encompasses amounts that differ due to different equilibrium conditions for a composition resulting from a particular initial mixture. Whether or not modified by the term “about”, the claims include equivalents to the quantities. The term “about” may mean within 10% of the reported numerical value, preferably within 5% of the reported numerical value.

As used herein, the term “embedded” means firmly enclosed by a surrounding mass.

As used herein, the term “monomer” means a molecule that can combine with others to form a macromolecule containing a large number of repeating units.

As used herein, the term “oligomer” means a linear or cyclic molecule containing from two (2) to about ten (10) repeating units derived from monomers. As used herein, the term oligomers refers to short chain polymers having relatively low molecular weight in comparison to the molecular weight of the final polymer.

As used herein, the term “condensation polymer” means any polymer that is generated via a condensation reaction in which a small molecule (e.g., water, hydrogen chloride, methanol, etc.) is eliminated during the formation of a covalent bond between two monomers, a monomer and an oligomer, or two oligomers. As used herein, the term “polymer” is intended to include copolymers.

The term “strike face” as used herein refers to the surface of the armor that faces away from the person wearing the armor or towards a hypothetical or real ballistic, threat or is otherwise the surface that is expected to be struck first by a projectile. The term “first strike section” as used herein refers to the section of the armor which comprises the strike face, and is typically the outermost surface of the armor.

The term “back face” as used herein refers to the surface of the armor that, when the armor is worn, is the surface that is closest to the body of the person wearing the armor. The term “body-facing section” as used herein refers to the section of the armor which comprises the back face.

The term “back face deformation” as used herein refers to the amount of rearward deformation the armor receives when struck by a non-penetrating projectile. Back face deformation, abbreviated herein as “BFD”, is also known in the art as “back face signature”. Although the projectile may not penetrate the armor, the part of the body to be protected which is directly behind the point of impact usually receives a “hammer-like” blow as a result of the deformation of the armor from the impact of the projectile. This blow can produce not only bruises and lacerations to the surface of the skin, but can produce damage to internal organs. Thus a reduction in the back face deformation of armor can correspond to reduced trauma to the body directly behind the point of projectile impact.

The term “stacked” as used herein describes the relative placement of plies of material in such a manner as to contact a surface of a first ply and a surface of a second ply placed upon the first ply. At least two plies of materials can be stacked together in the practice of the present invention. It can be desirable to maximize the contact area between the plies of materials that are stacked. In the case where the plies have the same shape, dimensions, and surface area, maximal contact between plies requires that one ply completely cover the ply that it contacts in the stack.

A ballistic resistant article, comprising:

(1) one or more woven fabric layers woven from yarns having a tenacity of at least 7.3 grams per dtex and a modulus of at least 100 grams per dtex; and (2) one or more sheet layers comprising a carbon nanotube-polymer composite, the composite comprising:

(a) randomly oriented carbon nanotubes entangled to form a planar structure, and

(b) a condensation polymer, wherein the randomly oriented carbon nanotubes are embedded in the condensation polymer; wherein:

(i) the composite comprises from about 15 weight percent to about 80 weight percent carbon nanotubes based on the combined weight of the carbon nanotubes and the condensation polymer; (ii) the woven fabric layers and the sheet layers are stacked together to form a core section comprising one or more woven fabric layers and one or more sheet layers; and (iii) the sheet layers comprise from about 0.25 weight percent to about 15 weight percent of the total weight of the article.

Fabric Layers

The fabric layers are woven. The term “woven” is meant herein to be any fabric that can be made by weaving; that is, by interlacing or interweaving at least two yarns, typically at right angles—but any conventional orientation of the weave is contemplated as within the scope of the present invention. Generally such fabrics are made by interlacing one set of yarns, called warp yarns, with another set of yarns, called weft or fill yarns. The woven fabric can have essentially any weave, such as plain weave, crowfoot weave, basket weave, satin weave, twill weave, and unbalanced weaves. In one embodiment, the woven fabric has plain weave.

In some embodiments, each woven fabric layer has a basis weight of from 50 to 800 g/m². In some embodiments, the basis weight of each woven layer is from 100 to 600 g/m². In some embodiments, the basis weight of each woven layer is from 130 to 500 g/m².

In some embodiments, the fabric yarn count is 5 to 100 ends per inch (2 to 39 ends per centimeter) in the warp, for example 8 to 60 ends/inch (3 to 24 ends per centimeter), or for example 10 to 45 ends/inch (4 to 18 ends per centimeter) in the warp. In some embodiments, the fabric yarn count in the weft or fill is 5 to 100 ends per inch (2 to 39 ends per centimeter), for example 8 to 60 ends/inch (3 to 24 ends per centimeter), or for example 10 to 45 ends/inch (4 to 18 ends per centimeter).

In some embodiments, the woven fabric layers are not encased or coated with a matrix resin; in other words, the woven fabric layers are matrix resin free.

In some embodiments, the woven fabric layers are coated with a matrix resin. By “matrix resin” is meant an essentially homogeneous resin or polymer material in which the yarn is embedded. The polymer of the matrix resin can be any polymer that provides the required level of adhesion with the fabric. Polymeric resins suitable for use with the fabric layers include polyvinyl butyral phenolic, polyesters, polyolefins (polyethylene, polypropylene, polybutylene and copolymers and blends of these), polyetheramides, fluoropolymers, polyethers, celluloses, phenolics, polyesteramides, polyurethanes, epoxies, aminoplastics, silicones, polysulfones, polyetherketones, polyetheretherketones, polyesterimides, polyphenylene sulfides, polyether acryl ketones, poly(amideimides), polyimides, polystyrene copolymers, polyamides, vinylesters, and blends thereof. In one embodiment, the matrix resin comprises either a thermoplastic resin or a blend thereof, or a thermosetting resin, or a blend thereof, but not both a thermoplastic and a thermosetting resin together as disclosed in published patent application US 2001/0113534, which is incorporated herein by reference. In one embodiment, the matrix resin can comprise an acid ethylene copolymer disposed between at least two of the fibrous fabric layers, wherein the ethylene copolymers are neutralized with an ion as disclosed in published patent application US 2001/0113534.

In some embodiments, the woven fabric layers are free from any matrix resin.

The fabric layers are woven from multifilament yarns having a plurality of filaments. The yarns can be intertwined and/or twisted. For purposes herein, the term “filament” is defined as a relatively flexible, macroscopically homogeneous body having a high ratio of length to width across its cross-sectional area perpendicular to its length. The filament cross section can be any shape, but is typically circular or bean shaped. Herein, the term “fiber” is used interchangeably with the term “filament”, and the term “end” is used interchangeably with the term “yarn”.

The filaments can be any length. Preferably the filaments are continuous. Multifilament yarn spun onto a bobbin in a package contains a plurality of continuous filaments.

The yarns have a yarn tenacity of at least 7.3 grams per dtex and a modulus of at least 100 grams per dtex. In one embodiment, the yarns have a linear density of 50 to 4500 dtex, a tenacity of 10 to 65 g/dtex, a modulus of 150 to 2700 g/dtex, and an elongation to break of 1 to 8 percent. In one embodiment, the yarns have a linear density of 100 to 3500 dtex, a tenacity of 15 to 50 g/dtex, a modulus of 200 to 2200 g/dtex, and an elongation to break of 1.5 to 5 percent.

The yarns may be made of filaments made from any polymer that produces a high-strength fiber. In some embodiments, the yarns are made of filaments made from a polymer selected from the group consisting of polyamides, polyolefins, polyazoles, and mixtures thereof.

When the polymer is polyamide, aramid is preferred. The term “aramid” means a polyamide wherein at least 85% of the amide (—CONH—) linkages are attached directly to two aromatic rings. Suitable aramid fibers are described in Man-Made Fibres—Science and Technology, Volume 2, Section titled Fibre-Forming Aromatic Polyamides, page 297, W. Black et al., Interscience Publishers, 1968. Aramid fibers and their production are, also, disclosed in U.S. Pat. Nos. 3,767,756; 4,172,938; 3,869,429; 3,869,430; 3,819,587; 3,673,143; 3,354,127; and 3,094,511.

In one embodiment, the aramid is a para-aramid. In one embodiment, the para-aramid is poly(p-phenylene terephthalamide), referred to herein as PPD-T. By PPD-T is meant the homopolymer resulting from mole-for-mole polymerization of p-phenylene diamine and terephthaloyl chloride and, also, copolymers resulting from incorporation of small amounts of other diamines with the p-phenylene diamine and of small amounts of other diacid chlorides with the terephthaloyl chloride. As a general rule, other diamines and other diacid chlorides can be used in amounts up to as much as about 10 mole percent of the p-phenylene diamine or the terephthaloyl chloride, or perhaps slightly higher, provided only that the other diamines and diacid chlorides have no reactive groups which interfere with the polymerization reaction. PPD-T, also, means copolymers resulting from incorporation of other aromatic diamines and other aromatic diacid chlorides such as, for example, 2,6-naphthaloyl chloride or chloro- or dichloroterephthaloyl chloride or 3,4′-diaminodiphenylether.

Additives can be used with the aramid and it has been found that up to as much as 10 percent or more, by weight, of other polymeric material can be blended with the aramid. Copolymers can be used having as much as 10 percent or more of other diamine substituted for the diamine of the aramid or as much as 10 percent or more of other diacid chloride substituted for the diacid chloride or the aramid.

When the polymer is polyolefin, polyethylene or polypropylene is preferred. The term “polyethylene” means a predominantly linear polyethylene material of preferably more than one million molecular weight that may contain minor amounts of chain branching or comonomers not exceeding 5 modifying units per 100 main chain carbon atoms, and that may also contain admixed therewith not more than about 50 weight percent of one or more polymeric additives such as alkene-1-polymers, in particular low density polyethylene, propylene, and the like, or low molecular weight additives such as anti-oxidants, lubricants, ultra-violet screening agents, colorants and the like which are commonly incorporated. Such is commonly known as extended chain polyethylene (ECPE) or ultra high molecular weight polyethylene (UHMWPE). Preparation of polyethylene fibers is discussed in U.S. Pat. Nos. 4,478,083, 4,228,118, 4,276,348 and Japanese Patents 60-047,922, 64-008,732. High molecular weight linear polyolefin fibers are commercially available. Preparation of polyolefin fibers is discussed in U.S. Pat. No. 4,457,985.

In some embodiments, the polymer for the yarn is polyazole. In one embodiment, the polyazole is a polyarenazole such as polybenzazoles and polypyridazoles. Suitable polyazoles include homopolymers and, also, copolymers. Additives can be used with the polyazoles and up to as much as 10 percent, by weight, of other polymeric material can be blended with the polyazoles. Also copolymers can be used having as much as 10 percent or more of other monomer substituted for a monomer of the polyazoles. Suitable polyazole homopolymers and copolymers can be made by known procedures, such as those described in or derived from U.S. Pat. Nos. 4,533,693; 4,703,103; 5,089,591; 4,772,678; 4,847,350; and 5,276,128.

In some embodiments, the polybenzazoles are polybenzimidazoles, polybenzothiazoles, and polybenzoxazoles. In some embodiments, the polybenzazoles are such that can form fibers having yarn tenacities of 30 gpd or greater. In one embodiment, the polybenzazole is a polybenzothioazole, for example poly(p-phenylene benzobisthiazole). In one embodiment, the polybenzazole is a polybenzoxazole, for example poly(p-phenylene benzobisoxazole) or the poly(p-phenylene-2,6-benzobisoxazole) called PBO.

In some embodiments, the polypyridazoles are polypyridimidazoles, polypyridothiazoles, and polypyridoxazoles. In some embodiments, the polypyridazoles are such that can form fibers having yarn tenacities of 30 gpd or greater. In some embodiments, the polypyridazole is a polypyridobisazole, for example poly(1,4-(2,5-dihydroxyl)phenylene-2,6-pyrido[2,3-d:5,6-d′]bisimidazole which is called PIPD. Suitable polypyridazoles, including polypyridobisazoles, can be made by known procedures, such as those described in U.S. Pat. No. 5,674,969.

Sheet Layers Comprising a Carbon Nanotube-Polymer Composite

The sheet layers comprise a carbon nanotube-polymer composite, the composite comprising randomly oriented carbon nanotubes entangled to form a planar structure and embedded in a condensation polymer. The carbon nanotubes are entangled, meaning that the nanotubes, or the ropelike structures typically formed by a plurality of nanotubes, are randomly twisted together and randomly overlaid to form a unitary network or arrangement of carbon nanotubes wherein the nanotubes are disordered and not woven together. Such carbon nanotube-polymer composites, and processes for making them, are disclosed in commonly-owned patent application having attorney docket number CL5989 USNP, filed concurrently herewith.

The carbon nanotubes have an average longest dimension in the range of about 1 micron to about 1000 microns. In some embodiments, the average longest dimension is between and optionally including any two of the following values: 1, 5, 10, 15, 25, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 microns. The carbon nanotubes comprise single wall nanotubes, multiwall nanotubes, or mixtures thereof. As used herein, a single wall carbon nanotube refers to a hollow carbon fiber having a wall consisting essentially of a single layer of carbon atoms. Single wall nanotubes are very flexible and naturally aggregate to form ropes of tubes. As used herein, a multiwall nanotube refers to multiple concentric sheets of hollow carbon fibers. Typically, multiwall nanotubes are formed as byproducts of single wall carbon nanotube syntheses. In some embodiments, the carbon nanotubes comprise single wall nanotubes, multiwall nanotubes, or mixtures thereof, and the carbon nanotubes have an average longest dimension in the range of about 1 μm to about 1000 μm.

The carbon nanotubes are embedded in a condensation polymer comprising polyester, polyamide, polyaramid, or polyacetal. The carbon nanotube-polymer composite is nonporous and well consolidated, meaning that the nanostructured sheet of entangled carbon nanotubes and the condensation polymer are combined into a single unitary layer. In one embodiment, the carbon nanotube-polymer composite is a carbon nanotube-polyester composite. In one embodiment, the polyester comprises polybutylene terephthalate. In one embodiment, the carbon nanotube-polymer composite is a carbon nanotube-polyamide composite. In one embodiment, the carbon nanotube-polymer composite is a carbon nanotube-polyaramid composite. In one embodiment, the carbon nanotube-polymer composite is a carbon nanotube-polyacetal composite.

In some embodiments, the weight percent of the carbon nanotubes in the carbon nanotube-polymer composite, based on the weight of the carbon nanotubes and the condensation polymer, is between and optionally including any two of the following values: 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, and 80 weight percent. In some embodiments, the weight percent of the nanotubes is from about 35 weight percent to about 75 weight percent, or from about 40 weight percent to about 60 weight percent, based on the weight of the carbon nanotubes and the condensation polymer. In some embodiments, the carbon nanotube-polymer composite is a carbon nanotube-polyester composite, and the weight of the nanotubes is from about 40 weight percent to about 60 weight percent. In some embodiments, the polyester comprises polybutylene terephthalate and the weight percent of the nanotubes is from about 40 weight percent to about 60 weight percent.

In some embodiments, the areal density of the carbon nanotube-polymer composite is in the range of about 5 grams per square meter to about 100 grams per square meter, for example in the range of about 10 grams per square meter to about 50 grams per square meter.

The carbon nanotube-polymer composites are formed by in situ polymerization under suitable conditions of appropriate condensation polymer precursors in the presence of the entangled sheet of carbon nanotubes. Suitable polymerization conditions include sufficient pressure, temperature, time, and other process conditions for polymerization of the polymer precursors to occur. Optionally, suitable polymerization conditions can include addition of a catalyst.

The carbon nanotube-polymer composite is made by a process comprising the steps:

(a) providing a porous mat comprising carbon nanotubes having an average longest dimension in the range of 1 micron to 1000 microns, wherein at least a portion of the carbon nanotubes are entangled;

(b) contacting the mat with one or more condensation polymer precursors, and optionally a catalyst;

(c) polymerizing the one or more polymer precursors in the presence of the mat at a temperature in the range of about 180° C. to about 360° C. to form a nonporous carbon nanotube-polymer composite comprising a mat of carbon nanotubes embedded in a condensation polymer produced from the polymer precursors, wherein the carbon nanotubes are present in the composite in an amount ranging from about 15 weight percent to about 80 weight percent, based on the weight of the carbon nanotubes and the condensation polymer; and

(d) optionally, curing the carbon nanotube-polymer composite.

As used herein, the term “mat” refers to a nanostructured sheet having a substantially planar form and comprising a plurality of entangled carbon nanotubes. Typically, a mat useful in the processes disclosed herein has a thickness in the range of about 10 microns to about 50 microns. Typically, a suitable mat has an areal density in the range of about 5 grams per square meter to about 100 grams per square meter and a porosity in the range of about 25% to about 85%, for example as measured by mercury intrusion porosity. A suitable mat can be obtained commercially or can be prepared by methods know in the art, for example by employing a chemical vapor deposition process or similar gas phase pyrolysis procedure to generate carbon nanotubes as disclosed in U.S. Pat. No. 7,611,579 and published patent application US 2012/0177926, or as disclosed in U.S. Pat. No. 7,993,620.

The porous mat comprising carbon nanotubes is contacted with one or more condensation polymer precursors, and optionally a catalyst. Under polymerization conditions, the condensation polymer precursors undergo in situ polymerization to produce a condensation polymer which forms the polymer component of the carbon nanotube-polymer composite. The composite is nonporous as a result of the condensation polymer occupying the openings previously present between adjacent nanotubes, or between adjacent ropelike structures of nanotubes, within the mat. In one embodiment, the condensation polymer precursors comprise monomers, oligomers, or mixtures of monomers and oligomers.

In one embodiment, the mat is contacted with condensation polymer precursors comprising a diacid or a diester, and a diol, and the polymer precursors are polymerized in the presence of the mat to form a carbon nanotube-polyester composite. Useful diacid or diester polymer precursors include aliphatic dicarboxylic acids which contain from 4 to 36 carbon atoms, diesters of aliphatic dicarboxylic acids which contain from 6 to 38 carbon atoms, aryl dicarboxylic acids which contain from 8 to 20 carbon atoms, diesters of aryl dicarboxylic acids which contain from 10 to 22 carbon atoms, alkyl substituted aryl dicarboxylic acids which contain from 9 to 22 carbon atoms, or diesters of alkyl substituted aryl dicarboxylic acids which contain from 11 to 22 carbon atoms. In one embodiment, the aliphatic dicarboxylic acids contain from 4 to 12 carbon atoms. Some representative examples of such aliphatic dicarboxylic acids include glutaric acid, adipic acid, and pimelic acid. In one embodiment, the diesters of alkyl dicarboxylic acids contain from 6 to 12 carbon atoms. In one embodiment, the aryl dicarboxylic acids contain from 8 to 16 carbon atoms. Some representative examples of aryl dicarboxylic acids are terephthalic acid, isophthalic acid, and orthophthalic acid. In one embodiment, the diesters of aryl dicarboxylic acids contain from 10 to 18 carbon atoms. Some representative examples of diesters of aryl dicarboxylic acids include dimethyl terephthalate, dimethyl isophthalate, dimethyl orthophthalate, dimethyl naphthalate, and diethyl naphthalate. In one embodiment, the alkyl substituted aryl dicarboxylic acids contain from 9 to 16 carbon atoms. In one embodiment, the diesters of alkyl substituted aryl dicarboxylic acids contain from 11 to 15 carbon atoms.

Diol polymer precursors useful in preparing a polyester component of the present composite can comprise glycols containing from 2 to 12 carbon atoms, glycol ethers containing from 4 to 12 carbon atoms and polyether glycols having the structural formula HO-(AO)_(n)H, wherein A is an alkylene group containing from 2 to 6 carbon atoms and wherein n is an integer from 2 to 400. Generally, such polyether glycols will have a molecular weight of about 400 to 4000.

In one embodiment, the glycols contain from 2 to 8 carbon atoms. In one embodiment, the glycol ethers contain from 4 to 8 carbon atoms. Some representative examples of glycols which can be employed as a diol polymer precursor include ethylene glycol; 1,3-propylene glycol; 1,2-propylene glycol; 2,2-diethyl-1,3-propanediol; 2,2-dimethyl-1,3-propanediol; 2-ethyl-2-butyl-1,3-propanediol; 2-ethyl-2-isobutyl-1,3-propanediol; 1,3-butanediol; 1,4-butanediol; 1,5-pentanediol; 1,6-hexanediol; 2,2,4-trimethyl-1,6-hexanediol; 1,3-cyclohexanedimethanol; 1,4-cyclohexanedimethanol; and 2,2,4,4,-tetramethyl-1,3-cyclobutanediol. A representative example of polyether glycol is Polymeg® and of polyethylene glycol is Carbowax®.

In another embodiment, the mat is contacted with condensation polymer precursors comprising cyclic oligomers of polyesters, and the polymer precursors are polymerized in the presence of the mat to form a carbon nanotube-polyester composite. Suitable cyclic oligomers of polyesters include cyclic poly(ethylene terephthalate) oligomer, cyclic poly(trimethylene terephthalate) oligomer, and cyclic poly(butylene terephthalate) oligomer. In one embodiment, the polymer precursor comprises cyclic poly(butylene terephthalate) oligomer. In one embodiment, the polymer precursor comprises cyclic poly(butylene terephthalate) oligomer and the polymer precursor further comprises a catalyst for polyester formation. Useful polyester oligomers are commercially available or can be prepared by methods known in the art; see, for example, U.S. Pat. No. 6,420,047.

Useful polyesters for the polymer component of the present composite include for example, poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), poly(trimethylene terephthalate) (3GT), and poly(trimethylene naphthalate)(3GN).

In one embodiment, the mat is contacted with condensation polymer precursors comprising a diacid and a diamine, and the polymer precursors are polymerized in the presence of the mat to form a carbon nanotube-polyamide composite. The diacid can be selected from aliphatic, alicyclic, or aromatic diacids. Specific examples of such acids include glutaric acid; adipic acid; suberic acid; sebacic acid; dodecanedioic acid; 1,2- or 1,3-cyclohexane dicarboxylic acid; 1,2- or 1,3-phenylene diacetic acid; 1,2- or 1,3-cylohexane diacetic acid; isophthalic acid; terephthalic acid; 4,4′-oxybis(benzoic acid); 4,4′-benzophenone dicarboxylic acid; 2,5-naphthalene dicarboxylic acid; and p-t-butyl isophthalic acid. In one embodiment, the polymer precursor for a carbon nanotube-polyamide composite comprises adipic acid.

Diamine polymer precursors useful in preparing a polyamide component of the present composite can be aliphatic, alicyclic, or aromatic diamines. Specific examples of such diamines include hexamethylene diamine; 2-methyl pentamethylenediamine; 2-methyl hexamethylene diamine; 3-methyl hexamethylene diamine; 2,5-dimethyl hexamethylene diamine; 2,2-dimethylpentamethylene diamine; 5-methylnonane diamine; dodecamethylene diamine; 2,2,4- and 2,4,4-trimethyl hexamethylene diamine; 2,2,7,7-tetramethyl octamethylene diamine; meta-xylylene diamine; paraxylylene diamine; diaminodicyclohexyl methane; and C₂-C₁₆ aliphatic diamines which can be substituted with one or more alkyl groups. In one embodiment, the polymer precursor for a carbon nanotube-polyamide composite comprises hexamethylene diamine.

Alternative precursors for preparing a polyamide component of a carbon nanotube/polyamide composite include compounds having a carboxylic acid functional group and an amino functional group, or a functional precursor to such a compound, which compounds include 6-aminohexanoic acid, caprolactam, 5-aminopentanoic acid, and 7-aminoheptanoic acid.

In one embodiment, the mat is contacted with condensation polymer precursors comprising an aromatic diacid or an aromatic acyl halide, and an aromatic diamine, and the polymer precursors are polymerized in the presence of the mat to form a carbon nanotube-aramid composite. Useful aromatic diacid or aromatic acyl halide polymer precursors include aryl dicarboxylic acids or acyl halides which contain from 8 to 20 carbon atoms. Suitable aryl dicarboxylic acid or acyl halides include terephthalic acid, terephthaloyl chloride, and terephthaloyl bromide. Aromatic diamine polymer precursors useful in preparing a polyamide component of the present composite include 1,4-phenyl-diamine and 1,3-phenyl-diamine.

In one embodiment, the mat is contacted with condensation polymer precursors comprising formaldehyde, a hemiformal of formaldehyde, trioxane, dioxolane, ethylene oxide, or mixtures thereof, and the polymer precursors are polymerized in the presence of the mat to form a carbon nanotube-polyacetal composite.

The relative amounts of the mat and the condensation polymer precursors are selected to provide a carbon nanotube-polymer composite containing carbon nanotubes in an amount ranging from about 20 weight percent to about 80 weight percent, based on the weight of the carbon nanotubes and the condensation polymer. In some embodiments, the composite contains an amount of carbon nanotubes between and optionally including any two of the following values: 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, and 80 weight percent, based on the weight of the carbon nanotubes and the condensation polymer. In some embodiments, the composite contains carbon nanotubes in an amount ranging from about 51 weight percent to about 80 weight percent, based on the weight of the carbon nanotubes and the condensation polymer. In some embodiments, the composite contains carbon nanotubes in an amount ranging from about 55 weight percent to about 80 weight percent, based on the weight of the carbon nanotubes and the condensation polymer. In some embodiments, the composite contains carbon nanotubes in an amount ranging from about 35 weight percent to about 75 weight percent, or from about 40 weight percent to about 60 weight percent, based on the weight of the carbon nanotubes and the condensation polymer.

Typically, when two or more polymer precursors are used to produce a carbon nanotube-polymer composite, the relative amounts of each polymer precursor are selected to achieve the desired stoichiometry in the condensation polymer produced. For example, in the case of a carbon nanotube-polyester composite, in one embodiment the condensation polymer precursors can comprise a diacid or diester as the first polymer precursor and a diol as the second polymer precursor, and the relative amounts of the first and second precursors are selected to be approximately equimolar. Amounts within about 10% of the desired equimolar ratio can also be used. Typically, condensation polymer precursors react to provide polymer in essentially quantitative yield. The water or alcohol generated during the condensation polymerization can be removed, for example by performing the polymerizing step at a pressure below atmospheric pressure, or by vaporization at polymerization temperatures. In one embodiment, at least a majority of the water or alcohol produced during the polymerization step is removed during the polymerization.

Optionally, the mat is contacted with one or more condensation polymer precursors in the presence of a catalyst. Suitable catalysts for condensation polymerizations are known in the art and are commercially available. For example, catalysts useful for polyester formation include strong acids, metal oxides and metallorganic complexes, including but not limited to phosphonic acid, ZrO₂, and organostannate complexes, respectively. Such catalysts are typically used in amounts ranging from about 0.01 mole percent to about 10 mole percent, for example from about 0.1 mole percent to about 2 mole percent, or from about 0.2 mole percent to about 0.6 mole percent based on total moles of monomer repeat units of the polymer precursor(s). In some embodiments, a catalyst is present in the contacting step and is combined with at least one of the polymer precursors.

When contacted with the mat comprising carbon nanotubes, the condensation polymer precursors can be in a solid form or a liquid or molten form. If used in the solid form, it is desirable for the polymer precursors to be used as finely granulated powders. Mixtures of solid and liquid polymer precursors can also be used. In some embodiments, the one or more polymer precursors have a melt viscosity in the range of about 0.1 s⁻¹ to about 10 s⁻¹ at a temperature in the range of about 180° C. to about 360° C.

The step of contacting the mat with one or more condensation polymer precursors can further comprise the steps of dissolving one or more of the condensation polymer precursors in a solvent to form a solution of the one or more polymer precursors, contacting the solution with the mat, and evaporating the solvent to leave the one or more polymer precursors in contact with the mat. Evaporating the solvent can be performed prior to polymerizing the polymer precursors, or concurrently with polymerizing the polymer precursors.

The polymerizing step is performed at a pressure below atmospheric pressure, for example inside a vacuum bag. In some embodiments, the polymerizing step is performed at a pressure above atmospheric pressure. In some embodiments, the pressure is between and optionally including any two of the following values: 170, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1250, 1500, 1750, 2000, 2250, 2500, 2750, 3000, 3250, 3500, 3750, and 4000 kPa. In some embodiments, the pressure is in the range of about 170 kPa to about 3500 kPa.

The polymerizing step is performed at a temperature in the range of about 180° C. to about 360° C. Typically, within this temperature range the polymer precursors are in the liquid state and impregnate the mat of carbon nanotubes, so that as the polymer precursors react to form the condensation polymer, the carbon nanotubes become embedded in the condensation polymer and the carbon nanotube-polymer composite is produced. In some embodiments, the temperature is in the range of about 180° C. to about 250° C. Heating can be provided by various means known in the art, including the use of microwaves.

The polymerization time can be between 2 minutes and 120 minutes. The appropriate amount of time varies depending upon conditions such as temperature, pressure, and the relative amounts of the polymer precursors and the mat of carbon nanotubes, and can be determined by one of ordinary skill in the art.

After the polymerization step, the carbon nanotube-polymer composite can be cured under suitable processing conditions, if desired. Typically, a curing step is performed in order to increase the molecular weight of the condensation polymer. A curing step can also ensure that the polycondensation reaction is driven to completion, thus minimizing residual monomeric or oligomeric polymer precursors. Suitable curing conditions include sufficient pressure, temperature, time, and other process conditions for an appropriate higher molecular weight to be achieved. In some embodiments, curing the carbon nanotube-polymer composite is performed at a pressure of about one atmosphere. In some embodiments, curing the composite is performed at a pressure greater than one atmosphere, for example up to about 276 MPa, or for example in the range from about 690 kPa to about 6895 kPa. In some embodiments, curing the composite is performed at a pressure below atmospheric pressure. In some embodiments, curing the composite is performed at a temperature in the range from about 120° C. to about 350° C. In one embodiment, a carbon nanotube-polyester composite is cured at a temperature ranging from about 120° C. to about 275° C., for example from about 160° C. to about 250° C. In some embodiments, curing the composite is performed for a time in the range of 1 minute to several hours.

Additional additives such as fillers for the adjustment of conductivity, pigments, and antioxidants, in powder or fibrous form, can be added to the carbon nanotube-polymer composite if desired, for example with the polymer precursors during the process of making the nanotube-polymer composite.

Each of the sheet layers has a thickness of at least 0.005 mm (0.1 mil), with the thickness of each of the sheet layers being typically from 0.005 mm to 0.100 mm (0.1-4 mil), for example 0.010-0.075 mm (0.4-3 mil) or for example 0.010-0.050 mm (0.4-2 mil). In some embodiments, each of the sheet layers has a thickness between about 0.01 mm and 0.1 mm. In some embodiments, each of the sheet layers has an average acoustic velocity of at least 1500 m/s, for example at least 2250 m/s, or at least 2500 m/s, or at least 2750 m/s, or at least 3000 m/s, or at least 3250 m/s. Average acoustic velocity can be measured according to ASTM E494.

Each of the sheet layers has a ratio of maximum strain to failure value to minimum strain to failure value of 1 to 4, for example 1 to 2 or even 1 to 1 when tested in accordance with ASTM method D882, meaning that the sheet layers are isotropic or substantially isotropic with regard to the ratio of maximum strain to failure value to minimum strain to failure value. As used herein, “substantially” means having a ratio of maximum strain to failure value to minimum strain to failure value of no greater than 4.

The sheet layers comprise 0.25 weight percent to 30 weight percent, for example 0.25 weight percent to 25 weight percent, or for example 0.25 weight percent to 20 weight percent, or for example 0.25 weight percent to 15 weight percent, or for example 0.25 weight percent to 10 weight percent, or for example 0.25 weight percent to 7.5 weight percent, or for example 0.25 weight percent to 5 weight percent of the total weight of the ballistic resistant article. In some embodiments, the sheet layers comprise 0.5 weight percent to 30 weight percent of the total weight of the ballistic resistant article. In some embodiments, the sheet layers comprise 0.25 weight percent to 5 weight percent of the total weight of the article.

Core Section

The woven fabric layers and the sheet layers stacked together comprise the core section. In one embodiment, the core section contains 1 to 60 of the woven fabric layers and 1 to 60 of the sheet layers. In one embodiment, the core section contains 3 to 30 of the woven fabric layers and 1 to 15 of the sheet layers. In one embodiment, the core section contains 3 to 15 of the woven fabric layers and 1 to 5 of the sheet layers. In one embodiment, the core section contains one of the woven fabric layers and one of the sheet layers. In some embodiments, the core section contains equal numbers of woven fabric layers and sheet layers. In some embodiments, the core section contains more woven fabric layers than sheet layers. Each of the woven fabric layers can be the same or different.

In one embodiment, the core section comprises a number of repeat units, each repeat unit comprising one or more woven fabric layers and one or more sheet layers. The number of repeat units can be from 1 to 60, for example from 1 to 30, or from 1 to 15, or from 1 to 10, or from 1 to 5. In some embodiments, the number of repeat units is from 1 to 10. In some embodiments, the repeat unit contains, in order, 1 to 5 of the woven fabric layers and 1 to 5 of the sheet layers. In one embodiment, the repeat unit contains, in order, one of the woven fabric layers and one of the sheet layers. In one embodiment, the repeat unit contains, in order, at least 2 of the woven fabric layers and one of the sheet layers. In some embodiments, the repeat unit contains more woven fabric layers than sheet layers. Each of the woven fabric layers of the repeat unit can be the same or different. In some embodiments, the core section comprises two or more different repeat units, each repeat unit comprising one or more woven fabric layers and one or more sheet layers.

The core section can have a woven fabric layer at one end and a sheet layer at the other distal end. Alternatively, the core section can have a woven fabric layer at each end.

Ballistic Resistant Article

The core section of the ballistic resistant article has a core first strike surface and a core body-facing surface. In some embodiments, the ballistic resistant article further comprises a first strike section and a body-facing section. The first strike section can comprise a plurality of the woven fabric layers stacked together and in contact with the core first strike surface. The body-facing section can comprise a plurality of the woven fabric layers stacked together and in contact with the core body-facing surface. In some embodiments, the first strike section contains 2 to 30 woven fabric layers stacked together and the body-facing section contains 2 to 30 woven fabric layers stacked together. If desired the woven fabric layers of the first strike section and the body-facing section can be the same or different.

FIG. 1 shows one embodiment of a ballistic resistant article as disclosed herein. The article 100 comprises, in order, a first strike section 115 having a strikeface 105, a core section 125 having a core first strike surface 130 and a core body-facing surface 135, and a body-facing section 120 having a backface 110. The first strike face section 115 comprises a plurality of woven fabric layers 155 stacked together and in contact with the core first strike surface 130 of the core section 125. In the embodiment shown, the core section 125 comprises four repeat units, each repeat unit 140 comprising one or more woven fabric layers 145 and one or more sheet layers 150. The body-facing section 120 comprises a plurality of woven fabric layers 165 stacked together and in contact with the body-facing surface 135 of the core section 125.

In one embodiment, the woven fabric layers and the sheet layers of the core section are attached together at 10% or less of their surface areas, allowing all or most of the remainder of the layers to move laterally and/or separate with respect to adjacent layers. In one embodiment, the woven fabric layers and the sheet layers are attached by less than 5%, for example less than 3%, of the surface area of the layers. The layers can be attached by stitches or adhesive or melt bonding, at edges and/or in the pattern of a cross (X), both as shown in FIG. 2, or in a pattern of squares typically done on a quilt, as shown in FIGS. 3, 4, and 5. The pattern of squares resulting from the quilting can be arranged parallel to the sides of the article, as shown in FIG. 4, or on a 45 degree bias relative to the sides of the article, as shown in FIGS. 3 and 5. The stitch pattern illustrated in FIG. 3 is referred to as a quilted stitch pattern with additional edge stitching. Referring to FIG. 4, when the stitch pattern is in squares, in one embodiment the stitch spacing 190 is from about 48 mm to about 100 mm, for example from about 50 mm to about 90 mm, or from about 60 mm to about 85 mm, or from about 70 mm to about 80 mm. “Stitch spacing” is defined as the distance 190 between adjacent parallel stitches in a stitch pattern of squares on the face of layers. In one embodiment, the stitch length 195 is from about 2 mm to about 7 mm, for example from about 3 mm to about 6 mm. “Stitch length” is defined as the shortest repeating length 195 of stitching yarn that transverses the face of the layer.

In some embodiments, the woven fabric layers and the sheet layers, stacked together, have an areal density between and optionally including any two of the following values: 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, and 6.5 kg/m². In some embodiments, the woven fabric layers and the sheet layers, stacked together, have an areal density between 3.0 and 5.5 kg/m².

In one embodiment, the ballistic resistant article has a backface deformation of less than or equal to 44 mm at a projectile velocity (V_(o)) of 1430 ft/sec plus or minus (+/−) 30 ft/sec (436 m/sec+/−9 m/sec) in accordance with NIJ Standard—0101.06 “Ballistic Resistance of Personal Body Armor”, issued in July 2008.

The ballistic resistant articles include protective apparel or body armor that protect body parts, such as vests or jackets, from projectiles. The term “projectile” is used herein to mean a bullet or other object or fragment thereof, such as, fired from a gun. The ballistic resistant articles disclosed herein provide improved protection against ballistic threats, for example by reduced backface deformation, without significantly increasing the weight or areal density of the body armor.

EXAMPLES

The processes described herein are illustrated in the following examples. From the above discussion and these examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications to adapt it to various uses and conditions.

The following abbreviations are used in the examples: “° C.” means degrees Celsius; “g” means gram; “g/m²” means grams per square meter; “psi” means pounds per square inch; “kPa” means kilopascal; “MPa” means megapascal; “GPa” means gigapascal; “psf” means pounds per square foot; “kg/m²” means kilograms per square meter; “fps” means feet per second; “m/s” means meters per second; “s” means second(s); “Ex” means Example, “Comp Ex” means Comparative Example; “Ave” means average, “CNT” means carbon nanotube; “mm” means millimeter(s); “cm” means centimeter(s); “μm” means microns; “m” means meter(s); “in” means inch(es); “PBT” means poly(butylene terephthalate).

Test Methods:

All temperatures were measured in degrees Celsius (° C.).

Linear Density: The linear density of a yarn or fiber is determined by weighing a known length of the yarn or fiber based on the procedures described in ASTM D1907-97 and D885-98. Decitex or “dtex” is defined as the weight, in grams, of 10,000 meters of the yarn or fiber. Denier (d) is 9/10 times the decitex (dtex).

Areal Density: The areal density of the fabric layer is determined by measuring the weight of each single layer of selected size, e.g., 10 cm×10 cm. The areal density of a composite structure is determined by the sum of the areal densities of the individual layers.

Average Acoustic Velocity: The acoustic velocity is the speed at which the tensile stress wave is transmitted through a material and is typically reported in m/s. Acoustic velocity can be measured in various directions and an average acoustic velocity can be calculated. When measured according to ASTM E494, the reported average acoustic velocity is the average value of acoustic velocities that are measured traveling radially from a point of impact in the sheet layer set at (0,0) at 0°, 45°, 90°, 135°, 180°, −45°, −90°, −135° with respect to the positive x axis, with the machine or roll direction positioned along the x axis and the cross or transverse direction positioned along the y axis.

Ballistic analysis: Ballistic tests of the ballistic articles were conducted using a 0.44 magnum semi-jacketed hollow point bullet (SJHP) based on the test protocol for NIJ Level IIIA as described in NIJ Standard—0101.06 “Ballistic Resistance of Personal Body Armor”, issued in July 2008. The reported V50 values represent the average value for two to six shots fired upon an article. The backface deformation (BFD) values represent the average value for two shots fired upon an article. BFD data were collected first, followed by V50 data, for the same article.

Materials and Processing:

All commercial materials were used as received unless stated otherwise.

Carbon nanotube (CNT) sheet articles of dimension 38.1 cm×38.1 cm (15 in×15 in) and areal density of 10±2.5 grams per square meter were received from Nanocomp Technologies, Inc. (Merrimack, N.H.). Cyclic poly(butylene terephthalate) oligomer powder containing a polymerization catalyst (CBT® 160) was received from Cyclics Corporation (Schenectady, N.Y.). CBT® 160 powder exhibits an initial melt viscosity of approximately 0.5 Pa·s at 190° C. The CBT® 160 powder was reduced to fine powder using a model LB10S Laboratory Blender from Waring Commercial (Torrington, Conn.) and particles of dimension ≦850 μm were isolated for use as the polymer precursor in Examples 1-9 via a #20 stainless steel testing sieve from VWR Intemational LLC (Bridgeport, N.J.). Tef-Lam Polytetrafluoroethylene (PTFE)-coated fiberglass laminate fabric (0.006″ thick), used as release paper, was cut from a 91.4 cm (36 in) wide roll received from CS Hyde Company (Lake Villa, Ill.). Tear & Crease Resistant fiberglass fabric coated with PTFE of thickness 0.025 cm (0.010 in), used as release paper, was cut from a 101.6 cm (40 in) wide roll received from CS Hyde Company (Lake Villa, Ill.). Ultra-Clean™ Supremium Aluminum Foil of dimension 45.7 cm×45.7 cm (18 in×18 in) and 0.076 mm (0.003 in) thick was cut from a 45.7 cm (18 in) wide roll received from VWR International LLC (Bridgeport, N.J.). Aluminum sheets of dimension 40.6 cm×40.6 cm (16 in×16 in) and 0.25″ thick were used as platens during hot pressing. Kevlar® 726G fabric (Kevlar® 129 yards of linear density 840 d woven in a plain weave at 26×26 ends per inch) was cut to dimension of 38.1 cm×38.1 cm (15 in×15 in) from a roll received from E.I. du Pont de Nemours and Co. (Wilmington, Del.). All cutting of PTFE-coated release paper and Kevlar® 726G was performed using N7250 series professional shears from Kia Scissors (Seattle, Wash.). An aqueous dispersion of ethylene/methacrylic acid co-polymer was prepared as follows: pellets of an ethylene copolymer containing approximately 20% by weight methacrylic acid that was approximately 60% neutralized by sodium cations (101 g) was added to water (500 mL) to yield a mixture with a solids concentration of 20.3 wt %. The mixture was then sonicated for 1 hour using a Vibra-Cell™ model VC750 probe sonicator equipped with a solid-tipped titanium alloy probe, all provided by Sonics & Materials, Inc. (Newtown, Conn.).

Hot-pressing: A multi-layer hydraulic press with four heated platens, model 100R24245-4HCS-P-Y 2 S8-R from PHI (City of Industry, CA), was used to hot-press CNT articles with CBT® 160 powder to generate CNT-polymer composite articles.

Article quilting: The ballistic articles of Examples 10, 11, and 12 were consolidated by quilting using a model LU-1508N industrial sewing machine from Juki Corporation (Tokyo, Japan). Kevlar® Gold NM 50/2 (315 denier) thread was used as received from Filtes International SRL (Capriolo, Italy). Ballistic articles of dimension 38.1 cm×38.1 cm (15 in×15 in) were quilted with the Kevlar® thread at a 45° bias with respect to the sides of the article in both the positive and negative direction, as shown in FIG. 5, in which the quilting stitches are represented as dashed lines on the face of the article. A line of thread was stitched into the article from one corner of the article to the opposite corner using 1 stitch per 3.18 mm (8 stitches per inch). Subsequent linear stitch lines were separated by 7.6 cm (3 in) from adjacent stitch lines.

Example 1 A Carbon Nanotube (CNT)-Poly(Butylene Terephthalate)

(PBT) composite of dimension 38.1 cm×38.1 cm (15 in×15 in) of areal density 21.4 grams per square meter (0.004 psf) containing 38.8 weight percent carbon nanotubes, based on the weight of the carbon nanotubes and the condensation polymer, was generated by hot-pressing a CNT sheet in the presence of cyclic poly(butylene terephthalate oligomer powder (CBT® 160) according to the following procedure. A square of aluminum foil of dimension 45.7 cm×45.7 cm (18 in×18 in) was cut from a roll of foil using scissors. From that square, an aluminum foil frame was generated by removing a smaller square of dimension 38.1 cm×38.1 cm (15 in×15 in) positioned at equidistance from all sides of the larger square, using a scalpel to cut the foil. Three squares of Tef-Lam PTFE-coated fiberglass laminate fabric of dimension 40.6 cm×40.6 cm (16 in×16 in) and one square of dimension 38.1 cm×38.1 cm (15 in×15 in) were cut from a roll of fabric using scissors. A total mass of 1.901 g of CBT® 160 powder was used.

FIG. 6 shows the configuration of the pressing package 40 used to consolidate the carbon nanotube mat and powdered PBT polymer precursor into a CNT-PBT composite in the hot press. Arrow 46 indicates the face of the lower aluminum platen 50 of the pressing package that was in contact with the face of the lower platen (not shown) of the hot press during consolidation; arrow 48 indicates the face of the upper aluminum platen 95 of the pressing package that was in contact with the face of the upper platen (not shown) of the hot press during consolidation. Two plies 55 and 60 of PTFE-coated fiberglass fabric (Tef-Lam fabric in Example 1) 40.6 cm×40.6 cm (16 in×16 in) were stacked one on top of the other and placed on the aluminum platen 50 of dimension 40.6 cm×40.6 cm (16 in×16 in). The aluminum foil frame 65 was laid upon the top ply 60 and adhered to the top ply 60 with a thin layer (not shown) of an aqueous dispersion of ethylene/methacrylic acid copolymer prepared as described above, such that a 38.1 cm×38.1 cm (15 in×15 in) area of ply 60 was exposed. Then the first half-portion of the total amount of CBT® 160 powder was distributed evenly across the exposed surface of ply 60 within the boundaries of the aluminum foil frame 65 to form the first powder layer 70. A CNT sheet 75 was then placed on top of powder layer 70. Next, the second half-portion of the total amount of CBT® 160 powder was evenly distributed across the CNT sheet 75 to form the second powder layer 80. A third ply 85 of PTFE-coated fabric 38.1 cm×38.1 cm (15 in×15 in) was placed on top of powder layer 80 within the boundaries of the aluminum foil frame 65. The final ply 90 of PTFE-coated fabric 40.6 cm×40.6 cm (16 in×16 in) was laid on top of ply 85 and a second 40.6 cm×40.6 cm (16 in×16 in) aluminum platen 95 was placed on top of ply 90 to form the pressing package 40.

The pressing package was inserted into a hot press pre-heated to 200° C. The press was closed until contact was made between the upper press platen and the pressing package. This position was held for 90 s without applying pressure to the pressing package, in order to bring the pressing package to the temperature of the hot press and to begin melting the CBT® 160 powder. The pressure applied to the package was then increased to 2.21 MPa (320 psi) and held at that pressure for 60 minutes. During this period, the CBT® 160 powder melted and polymerized, generating PBT, and the CNT-PBT composite was formed. Pressure was then released, the pressing package (now containing the CNT-PBT composite) was removed from the press, and the pressing package was quenched to room temperature in a water bath before separation from the Tef-Lam fabric. This CNT-PBT composite was utilized in the fabrication of a ballistic article in Example 10.

A CNT-PBT composite of dimensions 17.8 cm×17.8 cm (7 in×7 in), containing 39.8 weight percent carbon nanotubes based on the weight of the carbon nanotubes and the PBT, and made similarly to the composite of Example 1, was found to have an average sound wave velocity of 3408 m/s when measured according to ASTM E494.

A CNT-PBT composite of dimensions 2.54 cm×17.8 cm (1 in×7 in), thickness about 24 m, containing 40.1 weight percent carbon nanotubes based on the weight of the carbon nanotubes and the PBT, and made similarly to the composite of Example 1, was found to have a modulus of 7.94±1.08 GPa, a strength to break value of 149.0±54.7 MPa, and an elongation at break of 4.3±0.5 percent when measured according to the standard method ASTM D5034 “Breaking Strength and Elongation of Textile Fabrics—Grab Test” using an Instron Model 1122 Tensile Tester (Instron Corporation, Norwood, Mass.). The gauge length was 7.6 cm (3 in). The surfaces of those grips used for tensile testing were covered by a 1 cm (0.39 in) thick layer of rubber.

In Examples 2 through 9, additional CNT-PBT composites were prepared according to the procedure of Example 1, except as noted below. Table 1 summarizes the amounts of carbon nanotube mat and CBT powder used to prepare the composites of Examples 1-9.

Example 5

A CNT-PBT composite was prepared as described in Example 1, except that the highest applied pressure was 1.93 MPa (280 psi) instead of 2.21 MPa (320 psi).

Example 6

A CNT-PBT composite was prepared as described in Example 1, except that the highest applied pressure was 1.93 MPa (280 psi) instead of 2.21 MPa (320 psi).

Example 7

A CNT-PBT composite was prepared as described in Example 1, except that no aqueous dispersion of ethylene/methacrylic acid copolymer was used and the aluminum frame was placed directly on the Tef-Lam fabric.

Example 8

A CNT-PBT composite was prepared as described in Example 1, except that no aqueous dispersion of ethylene/methacrylic acid copolymer was used and the aluminum frame was placed directly on the Tef-Lam fabric.

Example 9

A CNT-PBT composite was prepared as described in Example 1, except that Tear & Crease Resistant fiberglass fabric was used instead of Tef-Lam fabric and no aqueous dispersion of ethylene/methacrylic acid copolymer was used, the aluminum frame was placed directly on the Tear & Crease Resistant fiberglass fabric.

TABLE 1 CNT-PBT Composites of Examples 1 through 9 Mass of Total mass of Areal Used in CNT mat CBT powder Wt % CNT in Density Ballistic Ex (g) (g) Composite (g/m²) Article of Ex 1 1.204 1.901 38.8 21.4 10 2 1.190 1.817 39.6 22.4 11 3 1.302 1.973 39.8 23.5 11 4 1.241 1.900 39.5 22.0 11 5 1.272 1.907 40.0 22.4 12 6 1.307 1.880 41.0 22.9 12 7 1.238 1.815 40.6 20.8 12 8 1.208 1.861 39.4 20.5 12 9 1.252 1.857 40.3 21.6 12

The composites of Examples 1 through 9 were used as described below in making the ballistic resistant articles of Examples 10, 11, and 12, each of which contained a first strike section, a core section, and a body-facing section.

Example 10

A stacked ballistic resistant article of dimension 38.1 cm×38.1 cm (15 in×15 in) was generated using a total of 28 Kevlar® 726G fabric plies and the CNT-PBT composite of Example 1. The plies were laid one upon the other in a stacked fashion, so that each ply was completely covered by the subsequent ply, to form the article 200 as shown in the cross-sectional view in FIG. 7. The article 200 contained, in order, a strikeface 205, a first strike section 215 consisting of 3 plies of Kevlar® 726G, a core section 220 consisting of one ply of Kevlar® 726G fabric 225 and the CNT-PBT composite generated in Example 1 as a single sheet layer 230, a body-facing section 235 consisting of 24 plies of Kevlar® 726G, and a back face 210. This article was then quilted as described above to consolidate the structure. The areal density of this article was 1.167 psf (5.693 kg/m²) and the weight percent of the CNT-PBT composite sheet layer was 0.5 of the total weight of the ballistic article. The V50 value of this article from six shots was 1544 feet per second (fps) and the backface deformation (BFD) value averaged from two shots was 43.0±2.3 mm. These values are tabulated in Table 2.

Example 11

A stacked ballistic resistant article of dimension 38.1 cm×38.1 cm (15 in×15 in) was generated using a total of 28 Kevlar® 726G fabric plies and the CNT-PBT composites of Examples 2, 3, and 4. The plies were laid one upon the other in a stacked fashion, so that each ply was completely covered by the subsequent ply, to form the article 300 as shown in the cross-sectional view in FIG. 8. The article 300 contained, in order, a strike face 305, a first strike section 315 consisting of 2 plies of Kevlar® 726G, a core section 320, a body-facing section 335 consisting of 20 plies of Kevlar® 726G, and a back face 310. The core section 320 consisted of, in order, 2 plies 325 of Kevlar® 726G, the CNT-PBT composite article of Example 2 as a single sheet layer 330, 2 plies 345 of Kevlar® 726G, the CNT-PBT composite article of Example 3 as a single sheet layer 350, 2 plies 355 of Kevlar® 726G, and the CNT-PBT composite article of Example 4 as a single sheet layer 360. The core section 320 of this article contained three repeat units, each repeat unit 385 consisting of, in order, two plies of Kevlar® 726G fabric and one CNT-PBT composite as a single sheet layer. Thus the core section of the ballistic article of Example 11 contained three sheet layers of a carbon nanotube-polymer composite separated by woven fabric layers. This article was then quilted as described above to consolidate the structure. The areal density of this article was 1.181 psf (5.766 kg/m²) and the weight percent of all the CNT-PBT composite sheet layers was 1.2 of the total weight of the ballistic article. The V50 value of this article from four shots was 1542 fps and the backface deformation (BFD) value averaged from two shots was 43.8±0.2 mm. These values are tabulated in Table 2.

Example 12

A stacked ballistic resistant article of dimension 38.1 cm×38.1 cm (15 in×15 in) was generated using a total of 28 Kevlar® 726G fabric plies and the CNT-PBT composites of Examples 5, 6, 7, 8, and 9. The plies were laid one upon the other in a stacked fashion, so that each ply was completely covered by the subsequent ply, to form the article 400 as shown in the cross-sectional view in FIG. 9. The article 400 contained, in order, a strike face 405, a first strike section 415 consisting of 2 plies of Kevlar® 726G, a core section 420, a body-facing section 435 consisting of 15 plies of Kevlar® 726G, and a back face 410. The core section 420 consisted of, in order, 2 plies 425 of Kevlar® 726G, the CNT-PBT composite article of Example 5 as a single sheet layer 430, 2 plies 445 of Kevlar® 726G, the CNT-PBT composite article of Example 6 as a single sheet layer 450, 2 plies 455 of Kevlar® 726G, the CNT-PBT composite article of Example 7 as a single sheet layer 460, 2 plies 465 of Kevlar® 726G, the CNT-PBT composite article of Example 8 as a single sheet layer 470, 3 plies 475 of Kevlar® 726G, and the CNT-PBT composite article of Example 9 as a single sheet layer 480. The core section 420 of this article contained four repeat units, each repeat unit 485 consisting of, in order, two plies of Kevlar® 726G fabric and one CNT-PBT composite as a single sheet layer, followed by, in order, three plies of Kevlar® 726G fabric and one CNT-PBT composite as a single sheet layer. Thus the core section of the ballistic article of Example 12 contained five sheet layers of a carbon nanotube-polymer composite separated by woven fabric layers. This article was then quilted as described above to consolidate the structure. The areal density of this article was 1.184 psf (5.781 kg/m²) and the weight percent of all the CNT-PBT composite sheet layers was 1.8 of the total weight of the ballistic article. The V50 value of this article from six shots was 1564 fps and the backface deformation (BFD) value averaged from two shots was 39.5±2.1 mm. These values are tabulated in Table 2.

Comparative Example A

A stacked comparative ballistic article of dimension 38.1 cm×38.1 cm (15 in×15 in) having 28 plies of Kevlar® 726G fabric and no sheet layers of a carbon nanotube-polymer composite was prepared as follows. The fabric plies were laid one upon the other in a stacked fashion, so that each ply was completely covered by the subsequent ply. The stack of plies was then quilted to consolidate the structure. The areal density of this article was 1.174 psf (5.732 kg/m²). The V50 value of this article from two shots was 1532 fps and the backface deformation (BFD) value averaged from two shots was 50.0±2.2 mm. These values are tabulated in Table 2.

TABLE 2 Construction^(a) of Ballistic Resistant Articles and Their Ballistic Resistance Perf

Construction^(b,c) First Body- Total # of Total # of Area strike facing fabric CNT-PBT Density V50 Ex section Core section^(a) Section layers layers (psf) (kg/m²) (fps) (n

10 3 K 1 K + Ex 1 24 K 28 1 1.167 5.693 1544 4

11 2 K 2 K + Ex 2 + 2 K + Ex 3 + 2 K + Ex 4 20 K 28 3 1.181 5.766 1542 4

12 2 K 2 K + Ex 5 + 2 K + Ex 6 + 2 K + Ex 7 + 15 K 28 5 1.184 5.781 1564 4

2 K + Ex 8 + 3 K + Ex 9 Comp — 28 K — 28 0 1.174 5.732 1532 4

Ex A Notes: ^(a)layers are listed in order of stacking, with those plies closest to the first strike section listed first ^(b)“K” refers to one ply of Kevlar ® 726G fabric ^(c)“Ex 1” refers to the CNT-PBT composite of Example 1; “Ex 2” refers to the CNT-PBT composite o

indicates data missing or illegible when filed

The data presented in Table 2 show the significant decrease in the backface deformation value of a ballistic protective article achieved by incorporation of a sheet layer comprising a carbon nanotube-polymer composite into the ballistic article. The backface deformation value for Comparative Example A, which contained only fabric layers, did not meet the 44 mm requirement set in NIJ Standard—0101.06 “Ballistic Resistance of Personal Body Armor”. However, using the same total numbers of fabric layers as in Comparative Example A and incorporating one, three, or five sheet layers comprising a carbon nanotube-polymer composite (Examples 10, 11, and 12, respectively) lowered the backface deformation value of those articles such that each article exhibited performance meeting the aforementioned NIJ Standard 44 mm requirement against at least one 0.44 magnum ballistic threat, while maintaining substantially the same areal density. 

What is claimed is:
 1. A ballistic resistant article, comprising: (1) one or more woven fabric layers woven from yarns having a tenacity of at least 7.3 grams per dtex and a modulus of at least 100 grams per dtex; and (2) one or more sheet layers comprising a carbon nanotube-polymer composite, the composite comprising: (a) randomly oriented carbon nanotubes entangled to form a planar structure, and (b) a condensation polymer, wherein the randomly oriented carbon nanotubes are embedded in the condensation polymer; wherein: (i) the composite comprises from about 15 weight percent to about 80 weight percent carbon nanotubes based on the combined weight of the carbon nanotubes and the condensation polymer; (ii) the woven fabric layers and the sheet layers are stacked together to form a core section comprising one or more woven fabric layers and one or more sheet layers; and (iii) the sheet layers comprise from about 0.25 weight percent to about 15 weight percent of the total weight of the article.
 2. The article of claim 1, wherein the yarns have linear density of 50 dtex to 4500 dtex, a tenacity of 10 g/dtex to 65 g/dtex, a modulus of 150 g/dtex to 2700 g/dtex, and an elongation to break of 1 percent to 8 percent.
 3. The article of claim 1, wherein the yarns are made of filaments made from a polymer selected from the group consisting of polyamides, polyolefins, polyazoles, and mixtures thereof.
 4. The article of claim 1, wherein the carbon nanotubes comprise single wall nanotubes, multiwall nanotubes, or mixtures thereof, and the carbon nanotubes have an average longest dimension in the range of about 1 μm to about 1000 μm.
 5. The article of claim 1, wherein the condensation polymer comprises polyester, polyamide, polyaramid, or polyacetal.
 6. The article of claim 5, wherein the polyester comprises polybutylene terephthalate and the weight percent of the nanotubes is from about 40 weight percent to about 60 weight percent.
 7. The article of claim 1, wherein the composite has an areal density in the range of about 5 grams per square meter to about 100 grams per square meter.
 8. The article of claim 1, wherein the composite has an average acoustic velocity of at least 2250 m/sec.
 9. The article of claim 1, wherein each of the sheet layers has a thickness between about 0.01 mm and 0.1 mm.
 10. The article of claim 1, wherein the sheet layers are isotropic or substantially isotropic with regard to the ratio of maximum strain to failure value to minimum strain to failure value.
 11. The article of claim 1, wherein the sheet layers comprise 0.25 weight percent to 5 weight percent of the total weight of the article.
 12. The article of claim 1, wherein the woven fabric layers and the sheet layers, stacked together, have an areal density between 2.5 to 6.5 kg/m².
 13. The article of claim 1, wherein the core section contains 1 to 60 of the woven fabric layers and 1 to 60 of the sheet layers.
 14. The article of claim 1, wherein the core section comprises a number of repeat units, each repeat unit comprising one or more woven fabric layers and one or more sheet layers.
 15. The article of claim 14, wherein the number of repeat units is from 1 to
 10. 16. The article of claim 14, wherein each repeat unit contains, in order, 1 to 5 of the woven layers and 1 to 5 of the sheet layers.
 17. The article of claim 1, wherein the core section has a first-strike surface and a body-facing surface, and wherein the article further comprises a first strike section and a body-facing section, the first strike section comprising a plurality of the woven fabric layers stacked together and in contact with the first-strike surface, and the body-facing section comprising a plurality of the woven fabric layers stacked together and in contact with the body-facing surface.
 18. The article of claim 17, wherein the first strike section contains 2 to 30 woven fabric layers stacked together and the body-facing section contains 2 to 30 woven fabric layers stacked together.
 19. The article of claim 1, wherein the article has a backface deformation of 30 less than or equal to 44 mm at a projectile velocity (V_(o)) of 1430 ft/sec plus or minus (+/−) 30 ft/sec (436 m/sec+/−9 m/sec) in accordance with NIJ Standard—0101.06 “Ballistic Resistance of Personal Body Armor”, issued in July
 2008. 